Currently, resonation devices utilizing MEMS (Microelectromechanical Systems) technology have been used as timing devices, for example. Such resonation devices are mounted on a printed circuit board of an electronic device, such as a smartphone. These resonation devices include a lower substrate, an upper substrate that forms a cavity between the lower substrate and the upper substrate, and a resonator disposed in the cavity between the lower substrate and the upper substrate.
An existing resonator including a plurality of vibration arms is disclosed, for example, in Patent Document (identified below). In the resonator disclosed in Patent Document 1, each of the vibration arms has an elongated shape, an end of the vibration arm near a base is a fixed end, and an end of the vibration arm away from the base is a free end. A mass portion (e.g., a hammer head or weight) is formed at the tip of the free end of the vibration arm. The mass portion has a larger cross-sectional area than a part of the vibration arm near the base. With the resonator described in Patent Document 1, by increasing the mass of the tip of the vibration arm, the frequency of bending vibration of the vibration arm can reduced, the length of the vibration arm can be reduced, and the size of the resonator can be reduced while maintaining a desired frequency value.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2012-105044.
However, as described in Patent Document 1, the capacitance of the resonator is reduced because the hammer head is formed at the free end of the vibration arm. As a result, the resonant resistance increases, and the oscillation efficiency of an oscillation circuit is reduced.